fitted a set of these last week......
the fitting in the back of the light housing is for a L.E.D. plug in number plate light. if you don't need it, fill the cavity with grease and cover with some good electrical tape. (would be nice if they supplied a cap)
the tails on the plugs are for clearance lights (or number plate light)
if you don't need them, put some dual wall heat shrink on each wire, but fold the end over and pinch it back on itself as it cools to seal the end.
plug them together and test, then use a larger diameter dw heatshrink over the connection (and the tails of the accessory wires) to make it completely waterproof.